Device for limiting a force to be conveyed by a lever effect

ABSTRACT

A device for limiting a force to be conveyed by a lever effect, especially torque wrench, with a handle having one end thereof provided with a support for the tool to be actuated, which support is rotatably or pivotably mounted, while a coupling connects the tool support to the handle until an adjustable force has been realized, whereupon after the set force has been exceeded a turning or pivoting of the tool support will occur. The coupling includes a hydraulic piston arrangement which comprises a main piston operable by the tool support or tool carrier, a control piston which against the thrust of a variable control spring is operable by pressure fluid displaced by the main piston, and a compensating piston which after a control bore is freed is displaced by the main piston against the thrust of a return spring.

Zerver [451 July 23,1974

DEVICE FOR LIMITING A FORCE TO BE CONVEYED BY A LEVER EFFECT Inventor: Hermann Jochen Zerver,

Reinshagener Str. 2, 5630 Remscheid, Germany Filed: July 3, 1973 Appl. No.: 376,129

Int. Cl. B25b Field of Search 81/524 R, 52.5

References Cited UNITED STATES PATENTS 5/1961 Eckman et al. 81/52.4 R 10/1962 Eckman 81/524 R 3/1963 Vilmerding et al. 81/524 R 11/1967 Amtsberg 81/524 R Lb 7o 7 10 14 a ng Primary Examiner-James L. Jones, Jr. Attorney, Agent, or FirmWalter Becker {57 ABSTRACT A device for limiting a force to be conveyed by a lever effect, especially torque wrench, with a handle having one end thereof provided with a support for the tool to be actuated, which support is rotatably or pivotably mounted, while a coupling connects the tool support to the handle until an adjustable force has been realized, whereupon after the set force has been exceeded a turning or pivoting of the tool support will occur. The coupling includes a hydraulic piston arrangement which comprises a main piston operable by the tool support or tool carrier, a control piston which against the thrust of a variable control spring is operable by pressure fluid displaced by the main piston, and a compensating piston which after a control bore is freed is displaced by the main piston against the thrust of a return spring.

10 Claims, 5 Drawing Figures jm ummmw 1 DEVICE FOR LIMITING A FORCETO BE CONVEYED BY A LEVEREFFECT The present invention relates toade'vicezforlimiting a force to be conveyed by; lever effect, especially torque wrench, with a handle having-one end thereof provided with a support-for'the tool tobe actuated.

which support is rotatably or pivotally mounted, such device being furthermore prov'idedw-ith a coupling which connects the tool carrier to the, handleuntil an adjustable force has been realizedwhereupon, after the set force has been exceeded, aturning or pivoting of the tool carrier relative to thehandle will bepossible.

Device adapted to be used as torque wrenches for" limiting a forceto be. conveyed byalever' effect are known which are provided with a'couplingwhichup to the realization of an adjustable-force establishes a rigid connection between the handle and the tool carrier which connection is made ineffective only after the. set force has been exceeded. With heretofore known torque wrenches of various types,: the. coupling force; is

always generated by springs. These springs have: the.

drawback that, after the set .force has been exceeded, they react instantaneously in a shock-like manner so that damage to the workpiece to be machined aswwell as injuries to the operator may occur.- A furtherdrawback of the heretofore known torquewrenchesis to. be seen in the fact that, in order to beableto. mount the springs, the tool must beof a considerablesiz'e, and that furthermore they cannot be so designed .as to, cover a sufficiently wide range for: the torqueseto. be set.

It is, therefore, an objectof thepresent invention to. improve the heretofore known devicesforlimiting'the force to be conveyed by a lever effectin such a way that with relatively little space requirements any desired wide range for the. forceto be overcome can .be-

tools will become effectiveinpa FIG. 2 is a top view similarto that'of FlG. 1 of-asec- 0nd embodiment of the invention.

FIG. 3 illustrates the torque wrench of FIG. Ztumed by 90 toward the viewer of FIG. 2.

FIG. 4 represents a top view and partially a section.

troduction to this specification, the device according to the present invention is characterized. primarily in that the coupling includes a hydraulic piston arrangement which comprises a main piston operable by- 100] carrier, a control piston which against the thrust ofa vari-. able control spring is operable'by' a pressure fluid by means of the main piston, and acompensating piston which after freeing a control bore is by means of the.

control piston displaceable by: the hydraulic fluid displaced by the main piston while overcominggthe thrust of a return spring.

According to afirst-embodiment of the invention, the control piston is providedwith avalve needle by means of which the control bore locatedbetween the pressure chamber of the mainpiston'andthe cylinder bore of the compensating piston can be closed. The control piston has in this connection to be displaced by a return linkage system against the thrust of the control spring when, followingthe release, thedevice is to be returned to. its positiongof (use; the return linkage protruding from the housing. To. avoidv the additional actuation of a return linkage, it is suggested, according to a further development of the. invention, to provide a springloaded check valve adapted to be opened in the direction toward the pressure chamber, this check .valve being arranged betweenthe pressure chamber of the main piston and thecylinder bore of the compensating piston,

For simplifying the machining of the hydraulic block for receiving the three pistons, the control piston is in conformity with a further feature of the invention designed as valve. needle which is arranged coaxially within the compensating piston and is displaceable in dependently of the compensating piston. In view of this coaxial position, it is not necessary toprovidea special bore for the control piston so that in view of this feature also the space requirementof' the device can be reduced;

According-tea preferred embodiment of the invenand on the other end carries the tool carrier. The tool carrier is, in conformity with the present invention, exchangeably connected to alever which is pivotally mounted on the housing and has its free end connected to the main-piston. Expediently, the tool carrier is designed in the manner of a ratchet wrench. The ratchet lever of this wrench is insertable into a bearing member which is rotatably. mountedin the housing in such a way that the free end of the ratchet lever cooperates with the main piston;

1 While. the abovecdescribed embodiment of the invention requires'a special housing which at one end carries the handle, the hydraulic arrangement may, according to a further embodiment of" the invention, be mounted directly in the handle. To this; end, according to a furtherfeature'ofthe invention, the main piston, on the one hand, and the controlp'istons arranged coaxially one within, the other as wellas the compensating pistons,.on the other hand, are arranged one behind the other ina handle housing. This. handle housing is pivotally connected with a bar which carries the tool carrier whilesone endface ofthis barhas an engaging surface for. the main piston which is provided with a piston rod.

According to apreferred embodiment of the invention, the main piston, on the one hand, and the control pistons coaxially arranged one within the other and the compensatingpistons, on the other hand, are together arranged along the'longitudinal central line of the handle housing.,The pivot point between the handle housing and the bar, is offset eccentrically. This design of the device according to the: present. invention requires the least space and additionally makesit possible to employ 3 differently long rods between the handle housing and the tool carrier which results in a further possibility of increasing the torque range to be covered by the device.

Referring now to the drawings in detail, the first embodiment of the invention, which is illustrated in FIG. 1, represents a torque wrench comprising a housing 1 which by means of a connecting rod 2 is provided with a handle 3. Rotatably joumalled in the housing 1 is a tool carrier 4 provided with a square head 4a. The tool carrier 4 adapted by means of its square head 4a to receive the respective tool is furthermore provided with an actuating lever 4b by means of which the tool carrier 4 rests against a coupling in the form of'a hydraulic'piston arrangement. This coupling is mounted in a hydraulic block 5 which is arranged in a recess 1a of housing 1. In this hydraulic block 5 there are arranged a main piston 6 provided with a piston rod 6a, a control piston 7 provided with a valve needle 7a, and a compensating piston 8. Whereas the main piston 6 and the control piston 7 are arranged one behind the other along a longitudinal central line, the compensating piston 8 islocated parallel and adjacentto the main piston 6. A returnspring19 is arranged in the cylinder bore 5b for the tip of the valve needle 7a arranged on the control piston 7 will normally close a control bore 11 which latter is provided between the pressure chamber 5a of. the

main piston 6 and the cylinder bore 5b of the compensating piston 8. v t

The control piston 7 is furthermore provided with a return rod system 12 which protrudes from the housing 1 to permit a manual pulling back of the valve needle 7a against the thrust of the control spring 10. The preload to which-the control spring is subjected can be adjusted by means of a set screw 14 which latter is provided with a scale or graduated drum 15. In order to permit a filling of the chambers receiving the hydraulic fluid, a closure screw 13 is arranged on the housing 1.

The operation of the torque wrench of FIG. 1 is as follows. To use the torque wrench for tightening screws or nuts at a pre'determined'desired torque, the square head 4a is provided with a'socket head. Moreover, by means of the set screw 14, the desired torque is set which can be read on the scale drum 15. Thereupon the torque wrench is applied and the handle 3 is pivoted in clockwise direction. During this pivoting operation, the lever 4b of the tool carrier 4 rests on the piston rod 6a of the main piston 6 which latter in this way will be subjected to a certain force in the direction toward the handle 3. This force generates an increase in pressure in the chamber 5a. As long as the pressure in the pressure chamber 5a is not able to displace the control piston 7 against the thrust of the control spring 10, a normal tightening of the screw or nut is effected. If, however, the force generated in the'pressure chamber 5a exceeds the counter force of the control spring 10, the

control piston 7 with the valve needle 7a is displaced which needle in this way will open the control bore 11. Consequently hydraulic fluid can now escape fromthe pressure chamber 5a of the main piston6'into the cylinder bore 5b of the compensating piston 6. As a result thereof, the piston 8 is displaced against the'thrustof the soft return spring 9 and in this way frees sufficient ton rod6a of the main piston 6, the withdrawal movement of the main piston 6 results in a turning of the square head 4a. The operator of the torquerwrench thus will notice the obtainment of the set torque by a soft and jerk-free yielding of the handle 3 in tightening direction.

To place the torque wrench in readiness for tightening the next screw or nut, it is merely necessary to withdraw the control piston equipped'with the valve needle 7a by means of the return linkage 12 against the thrust of the control spring 10 in order to open the control bore 11 for returning the hydraulic fluid into the pressure chamber 5a of the main piston 6. The control bore 11 had been closed by the valve needle 7a as soon 'as the pressure in the pressure chamber 5a had dropped. The return of the hydraulic fluid into the pressure chamber'Sa is effected automatically by the compensating piston 8 which is under the force of the return spring 9. I I Also with the second embodiment illustrated in FIGS. 2 and 3 of the present'invention, the torque wrench is equipped with a housing 16 which is provided with a handle 17 and in which various bores are provided for receiving the'three pistons. The cylindrical bores for receiving the pistons are, however, according to the second embodiment of the invention, located at a right angle with regard to the longitudinal axis of the housing 16. These bores are closed by 'ahousing cover 18 which by means of cover screws 18a is connected to the housing 16. y

The piston arrangement likewise comprises a main piston 19 equipped witha piston rod 19a, a control piston 20 anda compensating piston 21. With'the embodiment of FIG. 2, the control piston 20 is formed by the valve needleand iscoaxially arranged with regard to and within the compensating piston 21. The compensating piston 21 is again under the influence of the force of the return spring 22. The control piston. 20 which is provided with a collar 20a is under the load of a control spring 23 which latter is adjustable relative to the preload acting thereupon by a micrometer screw 24. The adjustment is facilitated by the arrangement of a graduated sleeve 25 and a graduated drum 26.

Thecontrol bore 27 is, according to the second embodiment of the invention,-arranged in the housing cover 18 which is provided with a transverse bore 28. This bore 28 establishes communication betwen the pressure chamber 16a of the main piston 19 and the cylinder bore 16b in which latter there are arranged the compensating piston 21 and the control piston 20. The transverse bore 28 additionally comprises a check valve 29 which opens in the direction toward the pressure chamber 16a of the 'main piston and which through a bore 29a communicates with the cylinder bore. 16b. The transverse bore 28 is closed by a closure .31 of which is inserted into a bearing member 32 which is rotatably mounted in one end of the housing 16 and is provided with an arresting screw 33. The free end of the ratchet lever 31 cooperates, in conformity with FIG. 2, with the piston rod 19a of the main piston 19 so that substantially the same operation is obtained as described in connection with the embodiment of FIG. 1.

The embodiment of FIG. 2 differs from that of FIG. 1 merely in that after the torque wrench has been removed from the completely tightened screw or nut, no actuation of the return linkage system is necessary in order to return the wrench to a new position of use because the hydraulic fluid displaced by the main piston 19 into the cylinder bore 16b of the compensating pis ton 21 will automatically through the check valve 29 flow back intothe pressure'chamber 16a as soon as the force exerted upon the handle 17 subsides.

According to the third embodiment of the invention which is illustrated in FIG. 4, the entire hydraulic system is arranged within a handle housing34 which by means of a link bolt 45 is pivotally mounted on a rod 46 the front end of which carries a ratchet wrench 47. The main piston 35 and the control pistons 36 coaxially arranged with regard to and within each other and the compensating piston 37 are located one behind the other in the handle housing 34. The control piston is again in the form of a valve needle and has a collar 36a for engagement with the control spring 39. The adjustment of the control spring 39 is effected by means of a micrometer screw 40 which is connected to a graduated drum 42. The pertaining graduated sleeve 41 rests on a threaded sleeve 40a which is screwed into the end of thecylinder bore 34b for the compensating piston 37 and the control piston 36. The communication of this cylinder bore 34 with the pressure chamber 34a for the main piston 35 is effected likewise bya control bore43 actuating bar of column-type drilling machines so that the force employed for longitudinally feeding the drill will be adjustable.

In view of the very short stroke of thecontrol piston, which stroke amounts to only a few tenth of a millimeter, a uniform precise function of the torque wrench will be realized which precise finction will not change even if the wrench is used frequently and for a longer period of time, because the control spring will, in view of the very slightspring stroke, not be subjected to any fatigue. t

As will be evident from the above, the device according to the present invention has the advantage that with a relatively small space requirement it can haveany desired high transmission ratio. This is due to the fact that r the three pistons which are interconnected by a hywhich is adapted to be closed by the tip of thecontrol.

piston 36 which latter is in the form of a valve needle. A bore extends parallel to the control bore 43 and has associated therewith a check valve 44 which latter opens in the direction toward the main piston when the pressure in the pressure chamber 34a is less than the pressure generated by the return spring 38 through the intervention of the compensating piston 37.

Also with the last mentioned torque wrench, a soft initiation which means a gradual pivoting of the handle housing 34 relative to the bar 46 occurs as soon as the set torque is exceeded. The return of the piston arrangement to its starting position is effected automatically in view of the check valve 44. t

The fourth embodiment according to FIG. 5 differs from the embodiment of FIG. 4 primarily in that the control piston 36 and the compensating piston 37 arranged coaxially with regard toeach other and one within the other, as well asthe main piston 35 are arranged along the longitudinal central line of the handle housing 34 so that the latter is provided with only one single bore. The control bore 43 and the check valve 44 are arranged in a control block 48 which is inserted into the bore of the handle housing 34. The main piston 35 which is provided witha seal 35a, held in its position by a nut 35b, is located within a cylinder bushing 49 which following the control block 48 is inserted into the bore of the handle housing 34.

The device illustrated in FIG. 5, the handle housing 34 of which is pivotally connected to a bar 46, can be employed not only as a torque wrench; for instance, it can also be employed for controlling a column-type draulic system can have the desired dirnentions so that also with a short lever arm sufficiently high torques can be exerted. In view of the employment of a hydraulic piston arrangement, also with increasing forces, a constant friction is obtained so that the force to be em ployed will not change or need not change. The freely selectable dimensions of each piston permit reducing of the forces for the control to such an extent that a weak and correspondingly precise control spring can be employed. The employment of a hydraulic system as coupling results in a soft release or initiation of the pivoting movement so that damage to the workpiece and injuries to the operator are for all practical purposes avoided.

It is, of course, to be understood that the present invention is, by no means, limited to the specific embodiments shown in the drawings but also comprises any modifications within the scope of the appended claims.

. What is claimed is:

1. A device equipped with a handle at one end thereof for limiting the transfer of a force by a lever effect, especially a torque wrench, which includes: supportingrneans pivotably arranged at the other end of said device for receiving a tool to be actuated, housing means, a main piston reciprocable in said housing means and movable hydraulically in one direction and movable in the opposite direction by said supporting means, a control piston reciprocable in said housing means, first conduit means for conveying liquid displaced by said main piston to said control piston for displacing the latter in a first direction, adjustable control spring means continuously urging said control piston in a second direction opposite to said first direction and operable to cause said control piston to close said first conduit means for preventing fluid communication between said main piston and said control piston, a compensating piston reciprocable in said housing means, second conduit means for establishing fluid communication between said control piston and said compensating piston, and return spring means urging said compensating piston to move in a first direction to a first position and yieldable in response to liquid displaced by said mainpiston and acting upon said compensating piston in a direction opposite to the direction of movement of said compensating piston to the said first position when the hydraulic pressure conveyed from said main piston to said compensating piston exceeds the thrust of said second spring means.

2. A device according to claim 1, which includes a valve needle associated with said control piston for closing said first conduit means.

3. A device according to claim 1, which includes resetting means protruding from said housing and operable manually against the thrust of said adjustable spring means for establishing communication between said main piston and said control piston through said first conduit means.

4. Advice according to claim 1, which includes check valve means interposed in said second conduit means, said check valve means opening in the direction toward said main piston.

5. A device according to claim 1, in which said control piston is formed by a valve needle and is arranged coaxially with and within said compensating piston, said control piston'being displaceable independently of said compensating piston.

6. A device according to claim 5, in which said mainpiston on the one hand and the control piston and the compensating piston which are arranged coaxially within each other on the other hand are parallel to each other and extend at a right angle to the longitudinal axis of said housing means.

7. A device according to claim 6, which includes a lever pivotally mounted on said housing and having its free end connected to said main piston, said supporting means being connected to said lever. I

8. A device according to claim 6, in which said supporting means is in the form of ratchet wrench, and which includes a bearing member detachably inserted in said housing means, said ratchet wrench having a lever rotatably joumalled in said bearing member for cooperation of the free end of said leverwith said main piston.

9. A device according to claim 1, in which said main piston on the one hand and the control piston and the compensating piston arranged coaxially within each other on the other hand are arranged in said handle, a supporting rod being provided which is pivotally connected to said suporting means while anend face of said rod serves as abutment surface for said main piston.

10. A device according to claim 9, in which said main piston on the one hand and the control piston and the compensating piston coaxially arranged within each other on the other hand are together arranged along the longitudinal central line of said handle, said handle and said rod being pivotally connected to each other while the pivot axis of said pivotal connection is offset eccentrically with regard to the longitudinal central line of said handle. 

1. A device equipped with a handle at one end thereof for limiting the transfer of a force by a lever effect, especially a torque wrench, which includes: supporting means pivotably arranged at the other end of said device for receiving a tool to be actuated, housing means, a main piston reciprocable in said housing means and movable hydraulically in one direction and movable in the opposite direction by said supporting means, a control piston reciprocable in said housing means, first conduit means for conveying liquid displaced by said main piston to said control piston for displacing the latter in a first direction, adjustable control spring means continuously urging said control piston in a second direction opposite to said first direction and operable to cause said control piston to close said first conduit means for preventing fluid communication between said main piston and said control piston, a compensating piston reciprocable in said housing means, second conduit means for establishing fluid communication between said control piston and said compensating piston, and return spring means urging said compensating piston to move in a first direction to a first position and yieldable in response to liquid displaced by said main piston and acting upon said compensating piston in a direction opposite to the direction of movement of said compensating piston to the said first position when the hydraulic pressure conveyed from said main piston to said compensating piston exceeds the thrust of said second spring means.
 2. A device according to claim 1, which includes a valve needle associated with said control piston for closing said first conduit means.
 3. A device according to claim 1, which includes resetting means protruding from said housing and operable manually against the thrust of said adjustable spring means for establishing communication between said main piston and said control piston through said first conduit means.
 4. Advice according to claim 1, which includes check valve means interposed in said second conduit means, said check valve means opening in the direction toward said main piston.
 5. A device according to claim 1, in which said control piston is formed by a valve needle and is arranged coaxially with and within said compensating piston, said control piston being displaceable independently of said compensating piston.
 6. A device according to claim 5, in which said main piston on the one hand and the control piston and the compensating piston which are arranged coaxially within each other on the other hand are parallel to each other and extend at a right angle to the longitudinal axis of said housing means.
 7. A device according to claim 6, which includes a lever pivotally mounted on said housing and having its free end connected to said main piston, said supporting means being connected to said lever.
 8. A device according to claim 6, in which said supporting means is in the form of ratchet wrench, and which includes a bearing member detachably inserted in said housing means, said ratchet wrench having a lever rotatably journalled in said bearing member for cooperation of the free end of said lever with said main piston.
 9. A device according to claim 1, in which said main piston on the one hand and the control piston and the compensating piston arranged coaxially within each other on the other hand are arranged in said handle, a supporting rod being provided which is pivotally connected to said suporting means while an end face of said rod serves as abutment surface for said main piston.
 10. A device according to claim 9, in which said main piston on the one hand and the control piston and the compensating piston coaxially arranged within each other on the other hand are together arranged along the longitudinal central line of said handle, said handle and said rod being pivotally connected to each other while the pivot axis of said pivotal connection is offset eccentrically with regard to the longitudinal central line of said handle. 